Even at the wide end of the backlash spectrum I wouldn't think there would be enough driveline lash to generate a complaint at least not in an old Chrysler product.
Just a thought: double-check your universal joints with the driveshaft removed at the pinion flange. Checking them with the shaft fully installed can be misleading due to binding. While you've got the shaft unbolted, check your pinion for wobble and in/out play. A bad pinion bearing can cause a similar complaint without causing audible gear whine. Then go try and wobble your slip yoke while it's still in the transmission to check the wear in the tailshaft bushing. There should be a little wiggle there, but not much. If the U-joints, pinion bearings, and slip yoke/tailshaft bushing check out, I'd agree with the others: don't mess with it. Yes, the backlash can be tightened up without resetting the whole rear, but it's a finesse job. It requires both the right tools and a solid familiarity with setting up the 8.75" in the first place. If you lack either, you're better off just living with it.
